Fossils from the Miura Peninsula and its Immediate North. 1 59 



left valve which is quite Hat has a few low but sharp-ridged 

 ribs. Very frequent, especially in the Miyata and Naganuma 

 Zones. 



Fossil occurrences. — Miyata Zone (Imori or Kutsukata in 

 Shimo-Miyata, Komatsugaike in Kami-Miyata and Motowada); 

 Yokosuka Zone (Otsu and Yokosuka); Naganuma Zone (Naga- 

 numa); Upper Musashino of Musashi, Shimosa and Kazusa. 



205. Pecten yessoensis, Jay. 

 Pl. XIII. Figs. 14, 15. 



Pecten yessoeyisis. Jay, Rep. on Shells coll. by Japan Exped., in Perry's Narrât, of Exped. 

 of Americ. Squadr. to China Seas and Japan, vol. VII, p. 293, pl. Ill, figs. 3, 4, pl. IV, figs. 1, 2. 

 Scheenck, Moll. d. Amurl. u. d. Nordjap. Meeres, p. 484, pl. XX, figs. 1-4. Lischke, Jap. 

 Meeresconch., I, p. 165, pl. X, figs. 3, 4, II, pl. XIII. Dünker, Index Moll., p. 240. Brauns, 

 Geol. Env. Tokyo, p. 48. Yokoyama, Pectens from the Koshiba Neogene, Jour. Geol. Soc. 

 Tokyo, vol. XXVin, no. 208, p. 2, pl. I, figs. 13, 14. 



Mostly in imperfect specimens. 



A recent shell which we got from the Hokkaido, 115 millim. 

 in height, is orbicular, inequilateral and radiately ribbed. The 

 right valve is tolerably convex with somewhat unequal ears, 

 while the left valve is nearly flat with ears equal. The ribs on 

 the right valve are about twenty-two, broad and flattish, sub- 

 equal, broader than the interspaces, now and then divided into 

 equal or unequal halves by a longitudinal groove. Those on the 

 left valve are somewhat more in number, also flattish towards the 

 ventral margin, but generally narrower than the interspaces. 



The fossil forms are all smaller than the above-described 

 recent one, so that the ribs number only between seventeen and 

 twenty-two. 



Fossil occurrence : — Miyata Zone (Shimo-Miyata); Kamaku- 

 ra Zone (Kewaizaka in Kamakura); Kanazawa Zone (Kanazawa); 

 Koshiba Zone (Koshiba); Upper Musashino of Musashi. 



Living: — Northern Japan; Ochotsk Sea. 



